How to Charge and When to Charge

[Chriull]

Just found a nice summary on http://batteryuniversity.com/learn/article/how_to_charge_when_to_charge_table (reduced to li-ion):

"

• Keep a battery at a moderate temperature. As food stays fresher when refrigerated, so also does cool temperature protect the battery by reducing internal corrosion, also known as parasitic reactions on the electrolyte and electrodes.
   
• Avoid deep cycling. Each cycle wears the battery down by a small amount and a partial discharge is better than a full discharge. Li-ion is maintenance-free and the battery lasts longest when operating between 30 and 80 percent SoC.
   
• Avoid abuse. Like a machine that wears down quicker under strenuous work, so also is a battery stressed by harsh discharges and rapid charges. Use cells that are optimized for the power and energy requirements as per application and increase that pack size to minimize load-related stresses.
   
• Avoid ultra-fast charge. Charge Li-ion Energy Cells at less than 1C (below rated Ah); Power Cells are more rugged and can be charged and discharged at a higher rate.
   
• Store Li-ion at partial charge in a cool place. The worst combination is high voltage and elevated temperature. Store Li-ion at approximately 50 percent SoC.

 

Frequently asked question	Lithium-ion (Li-ion, polymer)
How should I prepare a new battery?	Apply a topping before use. No priming needed
Can I damage a battery with incorrect use?	Keep partially charged. Low charge can turn off protection circuit
Do I need to apply a full charge?	Partial charge better than a full charge
Can I disrupt the charge cycle?	Partial charge causes no harm
Should I use up all battery energy before charging?	Deep discharge wears the battery down
Do I have to worry about “memory”?	No memory
How do I calibrate a “smart” battery?	Apply discharge/charge when the fuel gauge gets inaccurate. Repeat every 1–3 months
Can I charge with the device on?	Parasitic load can alter full-charge detection and overcharge battery or cause mini-cycles
Do I remove the battery when full?	Not necessary; charger turns off
How do I store my battery?	Store in cool place partially charged
Does battery heat up on charge?	Must stay cool or slightly warm
How do I charge when cold?	Do not charge below freezing
Can I charge at hot temperatures?	Do not charge above 50°C (122°F)
What should I know about chargers?	Battery must stay cool; no trickle charge when ready

"

 

 

 

 

[Bambino]

" 50 percent SoC."

 

What is "SoC"?

[Keith]

SOC is " State of Charge".

See also the below thread for a more detailed discussion:

 

[zlymex]

My charge method:

 1) Always charge to full after use. I don't believe the saying that 50% SoC is the best way to store the cells. I've tested many cells at 100% SoC and stored them for years and discharge them for capacity change. Here is an example of cells that discharge at 97% of the previous capacity after a year's storage.
http://bbs.38hot.net/forum.php?mod=viewthread&tid=12849&page=1#pid134516
This indicates that the capacity lost plus self-discharge is less than 3% after a year.
To make no misunderstanding, I charged it to full, discharge it by my electronic load to be 110.8Ah, charged it to full again, store it for one year, and discharged it again to give out 107.6Ah.

2) I often leave the charge on for several hours after the charge light is turn green(to balance the cells)

3) I Never hesitate to ride my GW to pedal tilt(5% left according to GW). Actually, after the tilt ride, the battery volt per cell is still above 3.35V meaning there is still a lot left(battery manufactures test cells to end at 2.8V or even 2.5V). Therefore, I'm unable to deep discharge the cells in my GW EUCs no matter what I do(unless I leave the EUC on for a very long time).

4) Never buy/use "smart" chargers, because it will cut off the charge completely and thus leave no charge current to balancing the cells.

[Keith]

1 hour ago, zlymex said:

 1) Always charge to full after use. I don't believe the saying that 50% SoC is the best way to store the cells. I've tested many cells at 100% SoC and stored them for years and discharge them for capacity change.

So what you are saying here is that Lithium Ion cells (I assume you ARE talking about LiIon cells - you do not say?) have a very low self discharge rate - that is something we knew already. What that confirms is there is absolutely no good reason to leave them at 100% as you have proved they don't lose much charge in storage so 40% storage charge would have been fine as well.

You also haven't said what temperature you stored them at? We also know that the higher the temperature the more harm is done.

Next if you have stored them for years,  then clearly you haven't used them. A brand new cell stored will behave considerably better than one that has had a significant number of charge cycles first.

Finally, you haven't looked at internal resistance. Leaving a battery fully charged at room temperatures will significantly increase its internal resistance as it ages.

On top of this, what appeared to be the greatest damaging mechanism on my batteries, was charging them to full and then storing them in a nice cool (frequently freezing) garage. That seemed to have exactly the same effect as overcharging them. Whereas, we know that cool, even freezing conditions are fine, indeed better for storing a LiIon battery that is at 40-50% charge.

I use an awful lot of Lithium Polymer batteries in model flying, everything from 1s 150mAh to 6S 6000mAh. Not one single battery lasted more than two years when I used to charge them to full as soon as possible after flying (I tend to fly only on a Saturday so they would then sit is a garage for a week at least, sometimes months if they didn't fit the planes that were in favour at the time.)

Once I better understood the batteries, I always leave them at 3.8V/cell if they are not going to be used for a while. I haven't had a battery go high resistance on me in the last 4 years since I started doing that.

Finally, if 100% is perfectly OK, why have I never managed to purchase a LiIon or Lithium Polymer battery that has been at anything outside 3.7-3.85V per cell EVER, you are suggesting the manufacturers do not know what they are doing either.

[zlymex]

8 hours ago, Keith said:

You also haven't said what temperature you stored them at?

At room temperature.

8 hours ago, Keith said:

Finally, you haven't looked at internal resistance.

Yes I have. The tendency is increasing but not significant.

8 hours ago, Keith said:

I use an awful lot of Lithium Polymer batteries in model flying, everything from 1s 150mAh to 6S 6000mAh. Not one single battery lasted more than two years when I used to charge them to full as soon as possible after flying (I tend to fly only on a Saturday so they would then sit is a garage for a week at least, sometimes months if they didn't fit the planes that were in favour at the time.)

I think that true for Lithium Polymer batteries that they get swelled easily, even for no reason including storage at low SoC. Because of that, I seldom use this kind of batteries for more than two years.

8 hours ago, Keith said:

Once I better understood the batteries, I always leave them at 3.8V/cell if they are not going to be used for a while.

The thing is, I have so many batteries that I don't have time(or simply forgot) to discharge them to below 3.8V/cell after the test. Store batteries at 100% SoC making them ever ready for immediate use.

8 hours ago, Keith said:

Finally, if 100% is perfectly OK, why have I never managed to purchase a LiIon or Lithium Polymer battery that has been at anything outside 3.7-3.85V per cell EVER, you are suggesting the manufacturers do not know what they are doing either.

I didn't say 100% SoC is the best for storage, I just believe is not that significant compare to other %. And it is safer to transport below 50% SoC.